The present invention relates to an improved vacuum fluorescent display and a manufacturing method thereof, which enables a pattern to be arranged as desired, the vacuum state within the tube to be stable, and automation to enhance productivity.
Vacuum fluorescent displays can be classified according to the form of their connecting leads. For example, in a frame-lead type, leads are integrally formed with the frame as a single body, and in a pin-lead type, the leads are composed of a plurality of separate pins.
FIG. 1 illustrates a conventional vacuum fluorescent display of pin-lead type, partially exposed.
In the display tube, a vacuum is formed between a faceplate 1 and a substrate 2 with an interposing spacer 3. All of the functional parts of the display are provided on the substrate 2. The following components can be given as examples of the functional parts: a segment (not shown) placed on the substrate below a grid (to be described later) providing an alphanumeric pattern; a filament 5 arranged over the segment; a grid 6 positioned between the segment and filament 5 for controlling low-speed thermoelectron emission; a getter (not shown) for additional enhancement of the vacuum in the tube; and a contact spring for applying a negative potential to a transparent conductive layer 1' which is formed on the faceplate's inner surface to assist the effective concentration of electrons.
In this vacuum fluorescent display structure, the functional parts are divided into two groups, some are formed directly on the substrate while others are spaced from the first group and formed over the substrate. The latter group includes the grid 6 and filament 5. The grid 6 is installed above the substrate 2 at a predetermined height by contacts 6' at both ends thereof which are used for fixing the grid to the substrate and for electrical conduction. The filament 5 is positioned at the top portion of the functional layer by bridge-type supports 4 which are provided at both edges of the inner surface of substrate 2.
Meanwhile, in order to operate, the functional layer must be supplied with external control voltages and provided with internal electrical circuits formed on the functional layer. To accomplish this, a plurality of exposed contacts 2' along the edge of substrate 2 form signal paths. At this time, a pin-lead 8 with U-shape clamps 8' is used for convenient connecting with a driving circuit on a separate printed circuit board. Respective pin-leads 8 arranged in a row along one edge of substrate 2 are engaged with the exposed contacts 2', and are permanently fixed by a sealing material such as frit glass 7.
In FIG. 2, a conventional frame-lead type vacuum fluorescent display is illustrated, which has similar functional parts as the foregoing pin-lead type vacuum fluorescent display. In more detail, all of the functional parts are provided on a substrate 2 below a faceplate 1 which together with substrate 2, encases a vacuum space. The functional layer includes an alphanumeric segment, a filament 5 disposed above the segment, and a grid 6 positioned between the segment and filament 5 for controlling low-speed thermoelectron emission.
Here, filament 5 and grid 6 are directly connected to the inner ends of selected leads 8b which are bent as crank and arranged parallel with one another along one edge of the substrate, different from the fixing construction of the pin-lead type. More specifically, grid 6 is fixed overlying the inner fixed end 8b' of lead 8b bent as crank, and the filament 5 is fixed by interposing a stand 4b with welding stop 4b' by the leads 8b placed at both ends. On the other hand, the segment makes contact with the inner end 8b" of other leads 8b of inverted "V" shape through the corresponding signal line connector 2", thereby forming an electrical circuit.
According to the above-described lead characteristics, the two aforementioned conventional vacuum fluorescent displays have merits and demerits as follows.
Since the functional layer pattern is independent of the shape of the lead, the pin-lead type vacuum fluorescent display offers a wide choice in selecting patterns of the functional layer, and it's vacuum tube has low probability of leakage. However, while the assembling jigs are simple, the process for manufacturing and assembling the leads is fastidious due to using a plurality of separate pin-type leads. Furthermore, the substrate may be damaged while fixing the leads, which makes automation in manufacturing the product difficult.
As for the frame-lead type vacuum fluorescent display, the functional part placed over the substrate such as the metallic components including the grid and filament is first fixed to the frame lead, separately from the substrate, and then is fixed to the substrate. Therefore, this type of display takes very little time to manufacture, and is favorable for automation. Further, since the lead itself is used for direct electrical connection to the filament, grid, and segment, connections between circuits are very stable and accurate. However, the orientation of the grid is determined by the direction of the leads, which offers narrower choice in selecting the desired pattern. Particularly, since a predetermined width of the lead must enter the vacuum space, the seal is apt to leak. This type is also disadvantageous in that the frame lead is integrally formed with the filament contacts, grid contacts, and segment contacts, thus, the material cost is expensive. Moreover, the manufacturing process of the frame lead itself is necessarily accompanied by punching and pressing while considering the position and/or height of each component. Once manufactured, frame lead is restricted to a specific model, impeding common usage of components. During the assembling process, strict management of the size is required to secure a stable connection of each lead to the connectors as the functional part.